Aromatic polycarbonates, especially those based on bisphenol A [=2.2-bis-(4-hydroxyphenyl)-propane], have acquired outstanding importance as engineering plastics because of their excellent mechanical properties, their high electrical resistance and their unusually high heat resistance. They can essentially be produced in according with three different methods (compare H. Schnell, "Chemistry and Physics of Polycarbonates", Polymer Reviews, Vol. IX, page 27 et seq., Interscience Publ., 1964):
1. Using the melt trans-esterification process, so-called melt polycarbonates are obtained by melt trans-esterification of aromatic diphenols with diaryl carbonates under reduced pressure at temperatures of up to about 350.degree. C.
2. Using the solution process in a homogeneous phase (also referred to as the pyridine process), the diphenols are dissolved in organic bases such as pyridine, if appropriate with addition of inert organic solvents, and reacted with phosgene.
3. In the solution process in a disperse phase (the so-called two-phase boundary process), the alkali metal salts or alkaline earth metal salts of the diphenols are dissolved or suspended in an aqueous alkaline phase and reacted in the presence of an inert organic phase which preferably dissolves polycarbonate.
The polycarbonates produced according to processes 2 and 3 are described as solution polycarbonates. Melt polycarbonates and solution polycarbonates are distinguished by different properties: melt polycarbonates differ from solution polycarbonates in having a marked structural viscosity, better fire resistance higher resistance to hydrolysis and better bonding to glass fiber staple; furthermore, glass fiber-reinforced melt polycarbonate moldings can be manufactured with greater accuracy and exhibit less tendency to distortion than articles manufactured from solution polycarbonates. Solution polycarbonates are distinguished, compared to melt polycarbonates, by a lighter color and more advantageous mechanical properties, for example higher notched impact strength. The advantages of the solution polycarbonates manifest themselves particularly after the material has been aged.
Though polycarbonates in themselves, even without flameproofing additives, are classified amongst slow burning plastics, constant endeavors are made further to increase the flame resistance and in doing so particular attention must be given to the fact that the addition of certain halogen-containing compounds usually worsens the processability and mechanical properties.
DT-OS (German Published Specification) Nos. 1,930,257 and 2,253,072 and U.S Pat. No. 3,775,367 have disclosed polycarbonates of low flammability which contain alkali metal or ammonium perfluoroalkanesulphonates. DT-OS (German Published Specification) 2,049,358 and 2,113,987 and U.S. Pat. No. 3,836,490 have disclosed that polycarbonates containing alkali metal salts soluble in the polycarbonate melt -- where appropriate in combination with nickel salts -- exhibit greater flame resistance. DT-OS (German Published Specification) No. 2,149,311 has disclosed polycarbonates of low flammability, which contain alkali metal salts, which are insoluble in the polycarbonate melt, of inorganic acids and/or of phosphonic acids and/or such sulphonic acids as contain at least one CH bond. Furthermore, DT-OS (German Published Specification Nos. 2,148,598 and U.S. Pat. No. 3,845,007 have disclosed flameproof glass fiber-filled polycarbonate compositions of high impact strength which contain, in addition to 2-6% by weight of glass fibers, 0-3% by weight of chlorine and/or bromine and 0-10% by weight of alkali metal salts and/or nickel salts, and in which compositions the chlorine and/or bromine may have been introduced, for example, in the form of homopolycarbonates or copolycarbonates based on tetrachlorobisphenols or tetrabromobisphenols.
It was now the object of the invention to provide thermoplastic, high molecular aromatic polycarbonates which on the one hand are suitable for reinforcement by glass fibers and are of low flammability, but on the other hand also should possess excellent properties which are not inferior to those of the products which have not been rendered flame-resistant.